Polygalactomannans are polysaccharides that are found in the endosperm material of seeds from leguminous plants such as Cyamopsis tetragonoloba (guar gum), Cesalpinia spinosa (tara gum), Ceratonia siliqua (locust bean gum), and other members of the Leguminosae family. A polygalactomannan is composed of backbone of 1→4-linked β-D-mannopyranosyl units with recurring 1→6-linked α-D-galactosyl side groups branching from the number 6 carbon of a mannopyranose residue in the backbone. The galactomannan polymers of the different Leguminosae species defer from one another in the frequency of the occurrence of the galactosyl side units branching from the polymannopyranose backbone. The average ratio of D-mannosyl to D-galactosyl units in the polygalactomannan contained in guar gum is approximately 2:1, approximately 3:1 for tara gum, and approximately 4:1 for locust bean gum. Another important source of polygalactomannan is Cassia tora and Cassia obtusifolia (collectively known as cassia gum). The average ratio of D-mannosyl to D-galactosyl units in the polygalactomannan contained in cassia gum is approximately 5:1.
Polygalactomannan obtained from cassia gum is schematically represented in the structure below:
wherein n represents an integer from about 15 to about 35. In another embodiment, n represents and integer from about 20 about 30. In still another embodiment of the invention, the polygalactomannan of in invention has a number average molecular weight ranging from about 200,000 to about 300,000 (GPC method using a polystyrene standard)
Polygalactomannans are hydrocolloids that have a high affinity for water. They have been widely used as suspending, thickening, emulsifying, and gelling agents in applications as diverse as foodstuffs, coatings, personal care compositions and in oil well fracturing fluids. Although the use of these polymers has been met with great success, polygalactomannans used in their natural form have suffered some drawbacks from a water solubility standpoint. An unsubstituted polymannose backbone is completely insoluble in water. The attachment of galactose side units to the C-6 atom in the recurring mannose residues of the polymannose backbone increases the water solubility of the polymer, particularly in cold water (i.e., ambient temperature and below). The greater the galactose side unit substitution, the greater is the cold water solubility properties of the polygalactomannan. Consequently, lower ratios of D-mannosyl to D-galactosyl units in the polygalactomannan leads to better cold water solubility. For example the polygalactomannan contained in guar gum (average D-mannosyl to D-galactosyl ratio 2:1) is soluble in cold water, while the polygalactomannan obtained from cassia gum (average D-mannosyl to D-galactosyl ratio of 5:1) is only sparingly soluble in cold and hot water.
U.S. Pat. No. 4,753,659 to Bayerlein et al. discloses inter alia that improved cold water solubility can be imparted to cassia gum by chemically modifying the polygalactomannan. The reaction of cassia gum polygalactomannan with selected reagents to yield C-6 substituted derivatives is disclosed. Exemplary reaction products include C-6 substituted and unsubstituted alkyl ethers, C-6 substituted phosphate esters, and C-6 substituted quaternary ammonium compounds. Disclosed uses for the chemically modified cassia gum polygalactomannans include textile printing applications, oil well drilling auxiliaries, mining and explosive applications.
U.S. Pat. No. 5,733,854 to Chowdhary et al. discloses a chemically modified guar gum and a method for its preparation. According to Chowdhary et al., cationically derivatized guar gum polygalactomannans produce clear and colorless solutions upon dispersal in aqueous or organic solvents. A disclosed application for the cationically derivatized guar gum includes its incorporation into detergent compositions for human and household uses. Other disclosed uses include personal care and cosmetic applications. The use of cationically derivatized cassia gum in personal care, pharmaceutical, home care or cosmetic formulations is not discussed.
An inherent drawback with cationically derivatized guar gum polygalactomannans is the high ratio of galactose side units contained on the polymannose backbone. For every two mannose backbone repeating units there is one pendant galactose side unit. The galactose side units shield the hydroxyl groups contained on the C-6 atom of the mannose backbone units from access to derivation reagents. For the most part, only the C-6 hydroxyl group on the galactose side unit is accessible for functionalization by derivatizing agents. Consequently, the degree of cationic group substitution on the guar gum polygalactomannan is relatively low.
Accordingly, there exists is a need for a derivatized polygalactomannan with a high degree of molecular substitution which is suitable for use in thickener, stabilizer, emulsifier, spreading aid and carrier applications for enhancing the efficacy, deposition and delivery of chemically, cosmetically and physiologically active ingredients.